Conventionally approximately twenty kinds copper compound oxide superconductors with different crystal structures are known. Any of these copper compound oxide superconductors commonly includes, in its crystal structure, Cu-O.sub.2 sheets through which superconducting current flows, and a stratified structure composed of repeated units each including the Cu-O.sub.2 sheet and another layer situated at a predetermined distance therefrom.
In the case of the crystal structure of La.sub.2 CuO.sub.4, for example, repeated units each including an La.sub.2 O.sub.2 layer and a Cu-O.sub.2 sheet are arranged in layers in the direction of a c-axis (direction perpendicular to the Cu-O.sub.2 sheet), as shown in FIG. 1. In other words, one Cu-O.sub.2 sheet is sandwiched between earth two La.sub.2 O.sub.2 layers. This structure having one Cu-O.sub.2 sheet between the aforesaid layers, will be referred to as a one-layer system, hereinafter.
In the case of this crystal structure, there is a slip for a 1/2 unit cell in each La.sub.2 O.sub.2 layer with respect to the directions of a- and b-axes (directions within the plane of the Cu-O.sub.2 sheet). Crystallographically, therefore, two La.sub.2 O.sub.2 layers and two Cu-O.sub.2 sheets constitute a repeated unit.
One-layer system oxide superconductors of this type include, for example, Bi.sub.2 Sr.sub.2 CuO.sub.6, Tl.sub.2 Ba.sub.2 CuO.sub.6, Nd.sub.2 CuO.sub.4, and Pb.sub.2 SrLaCu.sub.2 O.sub.6+ .delta., which is described in "Physica C," vol. 166, 1990, pp. 502 to 512.
In the case of the crystal structure of Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub.7, moreover, repeated units each including a BaO-CuO-BaO layer, a first Cu-O.sub.2 sheet, a Y layer, and a second Cu-O.sub.2 sheet are arranged in layers in the direction of the c-axis, as shown in FIG. 2. Therefore, a unit composed of the first Cu-O.sub.2 sheet, Y layer, and second Cu-O.sub.2 sheet is sandwiched between each two BaO-CuO-BaO layers. This structure having two Cu-O.sub.2 sheets in the aforesaid unit will be referred to as a two-layer system, hereinafter.
In the case of this crystal structure, in contrast with the case of the aforementioned La.sub.2 CuO.sub.4, there is no slip with respect to the directions of tile a- and b-axes, so that the aforesaid repeated units are not different from crystallographic versions.
Two-layer system oxide superconductors of this type include, for example, Bi.sub.2 Sr.sub.2 Ca.sub.1 Cu.sub.2 O.sub.8, Tl.sub.2 Ba.sub.2 CaCu.sub.2 O.sub.8 described in "Nature", vol. 332, Mar. 31, 1988, pp. 420 to 422, YBa.sub.2 Cu.sub.4 O.sub.8 described in "Nature", vol. 334, July 14, 1988, pp. 141 to 143, Ba.sub.2 YCu.sub.3 O.sub.7-x described in "Japanese Journal of Applied Physics", vol. 26, No. 5, May, 1987, pp. L649 to La.sub.2-x Ca.sub.1+x Cu.sub.2 O.sub.6-x/2+ .delta. described in "Materials Chemistry", vol. 7, 1982, pp. 413 to 427, and Pb.sub.2 Sr.sub.2 (R, Ca).sub.1 Cu.sub.3 O.sub.8+y (R: rare earth element) described in "Physica C", vol. 157, 1989, pp. 124 to 130.
In the case of the crystal structure of Bi.sub.2 Sr.sub.2 Ca.sub.2 Cu.sub.3 O.sub.10, repeated units each including a SrO-Bi.sub.2 O.sub.2 -SrO layer, a first Cu-O.sub.2 sheet, a first Ca layer, a second Cu-O.sub.2 sheet, a second Ca layer, and a third Cu-O.sub.2 sheet are arranged in layers in the direction of the c-axis, as shown in FIG. 3. Therefore, a unit composed of the first Cu-O.sub.2 sheet, first Ca layer, second Cu-O.sub.2 sheet, second Ca layer, and third Cu-O.sub.2 sheet is sandwiched between each two SrO-Bi.sub.2 O.sub.2 -SrO layers. This structure having three Cu-O.sub.2 sheets in the aforesaid unit will be referred to as a three-layer system, hereinafter.
Also in the case of this crystal structure, as in the case of the aforementioned La.sub.2 CuO.sub.4, there is a slip for a 1/2 unit cell in each SrO-Bi.sub.2 O.sub.2 -SrO layer with respect to the directions of the a- and b-axes. Crystallographically, therefore, the aforesaid two repeated units constitute a repeated unit.
Three-layer system oxide superconductors of this type include, for example, a Pb-Bi-Sr-Ca-Cu-O-based superconductor described in "Japanese Journal of Applied Physics", vol. 28, No. 5, May, 1989, pp. L787 to L790, a Tl-Pb-Sr-Ca-Cu-O-based superconductor described in "Science", vol. 242, October, 1988, pp. 249 to 252, and Tl.sub.1 Ca.sub.n-1 Ba.sub.2 Cu.sub.n O.sub.2n+3 (n=1, 2, 3) described in "Physical Review Letters", vol. 61, No. 6, August, 1988, pp. 750 to 753.
It is known that the greater the number of Cu-O.sub.2 sheets in each unit, in the aforementioned one-, two-, and three-layer system superconductors, the higher the superconducting transition temperature (Tc) of the materials.
The inventors hereof analyzed the correlations between the Tc of the copper oxide superconductors described above and the interlayer distances between the Cu-02 sheets in their crystal structures, and presented the results of this analysis in "Physica C", vol. 167, 1990, pp. 515 to 519.
Thereupon, the inventors hereof discovered that the shorter the interlayer distances between the Cu-O.sub.2 sheets of the crystal structures, the higher the value of Tc. In order to assign reasons for this phenomenon, the inventors hereof proposed that other layers interposed between the Cu-O.sub.2 sheets through which superconducting current flows should be classified into blocking layers and mediating layers as they are studied.
In this case, the blocking layer, in the crystal structure, may be regarded as a layer for cutting the interaction between the Cu-O.sub.2 sheets, through which the superconducting current flows, with the distance between the Cu-O.sub.2 sheets not shorter than 6 angstroms, and further supplying carriers to the Cu-O.sub.2 sheets to give the Cu-O.sub.2 sheets a function for a superconducting current flow. The mediating layer, which is interposed between the Cu-O.sub.2 sheets having -2-valent electric charge as a whole, may be regarded as a layer for neutralizing the electric charge, thereby enabling the whole crystal structure to be formed, and causing an interaction between the Cu-O.sub.2 sheets with the distance between them not longer than 4 angstroms.
From this point of view, the one-layer system oxide superconductor shown in FIG. 1 can be considered to be constructed so that one Cu-O.sub.2 sheet serving as a superconducting layer is sandwiched between each two identical La.sub.2 O.sub.2 blocking layers.
In the case of the two-layer system oxide superconductor shown in FIG. 2, on the other hand, two blocking layers are formed individually of identical BaO-CuO-BaO layers, and the unit composed of the first Cu-O.sub.2 sheet, Y layer as a mediating layer, and second Cu-O.sub.2 sheet, sandwiched between the blocking layers, functions as a superconducting layer.
In the case of the three-layer system oxide superconductor shown in FIG. 3, the unit composed of the first Cu-O.sub.2 sheet, first Ca layer as a first mediating layer, second Cu-O.sub.2 sheet, second Ca layer as a second mediating layer, and third Cu-O.sub.2 sheet sandwiched between each two identical SrO-Bi.sub.2 O.sub.2 -SrO(blocking) layers, and this unit functions as a superconducting layer.
Thus, according to the concept proposed by the inventors hereof, the crystal structure of the conventionally proposed copper oxide superconductors can be considered to be designed so that a superconducting layer is sandwiched between each two identical blocking layers, and it can be concluded that this superconducting layer is composed of one Cu-O.sub.2 sheet, or of two (for a two-layer system) or three (for a three-layer system) Cu-O.sub.2 sheets with a mediating layer between them.
If the conventionally known copper oxide superconductors are viewed at this angle, the blocking layers may be classified into the following 8 types:
La.sub.2 O.sub.2 -type, PA1 BaO-CuO-BaO-type, PA1 BaO-CuO-CuO-BaO-type, PA1 SrO-Bi.sub.2 O.sub.2 -SrO-type, PA1 BaO-Tl.sub.2 O.sub.2 -BaO-type or BaO-TlO-BaO-type, PA1 SrO-PbO-Cu-PbO-SrO-type, PA1 SrO-(Pb, Cu)O-SrO-type or SrO-(Pb, Sr)O-SrO-type, PA1 Ln.sub.2 O.sub.2 -type (Ln is selected from Nd, Sm, Eu, and Gd). PA1 La.sub.2 O.sub.2, PA1 BaO-CuO-BaO, PA1 BaO-CuO-CuO-BaO, PA1 SrO-Bi.sub.2 O.sub.2 -SrO, PA1 BaO-Tl.sub.2 O.sub.2 -BaO, PA1 BaO-TlO-BaO, PA1 SrO-PbO-Cu-PbO-SrO, PA1 SrO-(Pb, Cu)O-SrO, and PA1 SrO-(Pb, Sr)O-SrO. PA1 La.sub.2 O.sub.2, PA1 BaO-CuO-BaO, PA1 BaO-CuO-CuO-BaO, PA1 SrO-Bi.sub.2 O.sub.2 -SrO, PA1 BaO-Tl.sub.2 O.sub.2 -BaO, PA1 BaO-TlO-BaO, PA1 SrO-PbO-Cu-PbO-SrO, PA1 SrO-(Pb, Cu)O-SrO, PA1 SrO-(Pb, Sr)O-SrO, and PA1 Ln.sub.2 O.sub.2 PA1 La.sub.2 O.sub.2, PA1 BaO-CuO-BaO, PA1 BaO-CuO-CuO-BaO, PA1 SrO-Bi.sub.2 O.sub.2 -SrO, PA1 BaO-Tl.sub.2 O.sub.2 -BaO, PA1 BaO-TlO-BaO, PA1 SrO-PbO-Cu-PbO-SrO, PA1 SrO-(Pb, Cu)O-SrO, PA1 SrO-(Pb, Sr)O-SrO, and PA1 Ln.sub.2 O.sub.2 (where Ln is selected from Nd, Sm, Eu and Gd), PA1 1--1: BaO-CuO-BaO/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2, PA1 1-2: BaO-CuO-CuO-BaO/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2, PA1 1-3: BaO-CuO-CuO-BaO/Cu-O.sub.2 /BaO-CuO-BaO/Cu-O.sub.2, PA1 1-4: SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2, PA1 1-5: SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2 /BaO-CuO-BaO/Cu-O.sub.2, PA1 1-6: SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2 /BaO-CuO-CuO-BaO/Cu-O.sub.2, PA1 1-7: (BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2, PA1 1-8: (BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O.sub.2 /BaO-CuO-BaO/Cu-O.sub.2, PA1 1-9: (BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O.sub.2 /BaO-CuO-CuO-BaO/Cu-O.sub.2,, PA1 1-10: (BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O.sub.2 /SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2, PA1 1-11: SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2, PA1 1-12: SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2 /BaO-CuO-BaO/Cu-O.sub.2, PA1 1-13: SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2 /BaO-CuO-CuO-BaO/Cu-O.sub.2, PA1 1-14: SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2 /SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2, PA1 1-15: SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2 /(BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O.sub.2, PA1 1-16: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2, PA1 1-17: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /BaO-CuO-BaO/Cu-O.sub.2, PA1 1-18: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /BaO-CuO-CuO-BaO/Cu-O.sub.2, PA1 1-19: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2, PA1 1-20: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /(BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O.sub.2, PA1 1-21: ( SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2. PA1 2-1: BaO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2 /La.sub.2 O.sub.2 /M/Cu-O.sub.2, PA1 2--2: BaO-CuO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-3: BaO-CuO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-4: SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-5: SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-BaO/Cu-O.sub.O.sub.2 /M/Cu-O.sub.2, PA1 2-6: SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-7: (BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O.sub.2 /M/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-8: (BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-9: (BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-10: (BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O.sub.2 /M/Cu-O.sub.2 /SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2 /M/Cu-O .sub.2, PA1 2-11: SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-12: SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-13: SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-14: SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-15: SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-16: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-17: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-18: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-19: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-20: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /(BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O .sub.2 /M/Cu-O.sub.2, PA1 2-21: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-22: Ln.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2 //M/Cu-O.sub.2, PA1 2-23: Ln.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-24: Ln.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-25: Ln.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-26: Ln.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /(BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-27: Ln.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 2-28: Ln.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /(SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /M/Cu-O.sub.2. PA1 3-1: BaO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 3-2: BaO-CuO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 3--3: BaO-CuO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 3-4: SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O .sub.2, PA1 3-5: SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 3-6: SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-CuO-BaO/Cu-O.sub.2 /M/Cu-O=/M/Cu-O.sub.2, PA1 3-7: (BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2 /M/ Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 3-8: (BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 3-9: (BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O.sub.2 //M/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-CuO-BaO/Cu-O.sub.2 /M/Cu -O.sub.2 /M/Cu-O.sub.2, PA1 3-10: (BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO )/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O .sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 3-11: SrO-PbO-Cu-PbO-Sr/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 3-12: SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 3-13: SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 3-14: SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O .sub.2, PA1 3-15: SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /(BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 3-16: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O .sub.2 /M/Cu-O.sub.2, PA1 3-17: (SrO-Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2 / M/Cu-O.sub.2, PA1 3-18: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 3-19: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 3-20: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /(BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 3-21: (SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2 /M/Cu-O .sub.2 /M/Cu-O.sub.2, PA1 3-22: Ln.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /La.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 , PA1 3-23: Ln.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 3-24: Ln.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /BaO-CuO-CnO-BaO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 3-25: Ln.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /SrO-Bi.sub.2 O.sub.2 -SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu -O.sub.2, PA1 3-26: Ln.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /(BaO-Tl.sub.2 O.sub.2 -BaO) or (BaO-TlO-BaO)/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 3-27: Ln.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /SrO-PbO-Cu-PbO-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2, PA1 3-28: Ln.sub.2 O.sub.2 /Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2 /(SrO-(Pb, Cu)O-SrO) or SrO-(Pb, Sr)O-SrO/Cu-O.sub.2 /M/Cu-O.sub.2 /M/Cu-O.sub.2. PA1 Spectroscope: M-70, PA1 Light source: Halogen lamp, PA1 Sensor: Si and Ge, PA1 Polarizer and analyzer: Gran-Thomson PA1 Number of revolutions of analyzer: 2, PA1 Angie of incidence: 80.degree., PA1 Measurement wave-number: 7,000 to 25,000 cm.sup.-1,
and
Further, the mediating layer may be formed of Ca. Sr, Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, or Lu.
The materials of the one-layer system shown in FIG. 1 have blocking layers of only one kind except those ones which include Ln.sub.2 O.sub.2 -type blocking layers. In either of the two- and three-layer systems shown in FIGS. 2 and 3, moreover, the blocking layers in the crystal structures are of only one kind.
Accordingly, the conventional copper oxide superconductors are limited to about 20 kinds, so that fields of their industrial application are restricted.